The TRW
LT1001A
is no longer available; it was given to me years ago. I recently found
a letter in my files dated 1994 where Motorola said that the replacement for the LT1001A was the MRF5812. That's why I used the MRF5812 in
the 2 other preamps below.
The
2N5109
and some similar transistors will also work.

+12 volt DC feed through
2.5 mH RF choke - early design

Subsequent RF
chokes are made using ~5 turns of enameled wire through single
FB-73-801
bead

Two
back-to-back
1N914/1N4148 diodes from preamp input to ground also shown. Since this
photo
was taken, there are now four diodes, two in series in each direction.

There is now a small
incandescent lamp in series with the input to prevent damage from
nearby
transmitting antennas in proximity to the receive antennas.

The
pot shown is to reduce the input signal so that I can match the signal
levels while comparing different antennas. It's also in series with the
input. Approx. 2000 ohms. I use it to reduce the preamp gain so that the signals from the RX
antennas are similar in strength to the signals from the TX antenna.

The RF choke
shown in the schematic can be eliminated. It was for locating the
preamp remotely near the receive antenna (not usually necessary) and
feeding 12
VDC through the coax to power the preamp with a bias-tee arrangement
(two broadband RF chokes and two .1 uF disc ceramics).

Since I
created this page, this preamp now has the W7IUV emitter resistor
modification which further improves the 3rd order intercept and
compression points. W7IUV gives the following performance
specifications on his site:

"P1dB (1 dB output
compression power) should be greater than +21 dBm. Usually runs about
+24 to +27 depending on parts used.

"OIP3 (output
third order intercept point) should be +41 dBm or greater. I’ve
seen +44, which is as high as I can accurately measure with my test
setup."

Somewhere, he implied that the noise figure is about 6 dB. Likely, the
NF is lower without his emitter resistor mod; however, the IM3 is not
as good.

The increased current required a heat sink on the transistor, not shown
here.

There are
advantages to using a bipolar transistor over an FET or JFET. See the
above-referenced ARRL publication for more information.

I have only
ever used a TRW
LT1001A
in the original amplifier at the top of this page. It has slightly
better specs than the
2N5109. The LT1001A (now unobtanium) was offered for use in CATV
applications. The preamps below use
the surface-mount (SO-8) MRF5812.

Other W0BTU broadband
preamps based on same design, using MRF5812
NPN bipolar transistors. I probably built these sometime before
1995. The relays are to remotely switch the preamp in and out of the signal path.

I've
modified the one on the right since these photos were taken. They do
not (yet) have the W7IUV circuit mod, and out-of-band signals overload
it when connected directly to the feedpoint of my Beverage "pointed"
NW. That may be partly due to front-end protection diodes conducting.
Stay tuned.

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LINKS

www.w7iuv.comSchematic of improved
broadband preamp
using 2N5109, based on the same ARRL design. Click on the appropriate
link in the left column on
Larry's site to view his preamp page.